This invention relates to a method of and means for controlling the operation of a vehicle by means of electrical signals generated in a manner dependent on the road speed of the vehicle.
Signals so generated can be used in a wide range of applications such as speed warning devices, actuation of servo-mechanisms which could be used to control vehicle speeds, the monitoring of fuel consumption and, through the medium of a computer, more sophisticated controls between adjacent vehicles could be developed. All these applications are dependent on proper speed determination which will enable many computations involving vehicle speed and other variables to be achieved.
It is widely known that road speed related electrical signals can be obtained by monitoring the rotational movement of a component of the vehicle which moves proportionally to the road speed of the vehicle. This monitoring has been effected by the use of a photo-electric cell arrangement set up to observe a predetermined mark on a rotating component.
Also and more generally the monitoring has been effected by detecting the variation of a magnetic field associated with a rotating component of the vehicle and using this magnetic field variation to generate an electrical signal through the detector. The signal may be amplified and used to power or to trigger the particular vehicle control means for which the system has been designed.
Special devices to meet the requirements of individual installation have been made to work with reasonable success but the problem has always remained in that the wide variety of vehicles has heretofore made it practically impossible to provide a method and means which can be universally applied to all motor vehicles. Various methods known to the Applicants are the attachment of permanent magnets to wheel rims or drive shafts with the detecting or sensing heads located in just opposition thereto. These means are particularly susceptable to damage as they are outside the protective body of the vehicle and the installation of the detector has lead to difficult problems.
It has also been proposed to fit a drive shaft with a toothed wheel and having in close association therewith a magnetized magnetic sensor. This arrangement is subject to similar damage to that referred to above and the proposal is not possible with vehicles having only front wheel drive assemblies.
Also, there has been utilization of variations in magnetic flux caused by rotation of means producing a magnetic field associated with a speedometer cable. The latter method can involve the cutting of the speedometer cable to enable magnetic field producing means to be inserted between the cut ends. The disadvantage of sensing magnetic variations in this manner is that speedometer cables sometimes develope "whiplash", which results in erroneous speed sensing and monitoring.
There has also been the suggestion that the normally existing magnetic component in the vehicle speedometer be used to generate the signal in the sensor. In many of these cases serious accessibility problems arise in practical installations for different types of vehicles. Also different speedometers give rise to variations in frequencies of signals and types of fields.
Because it is essential that the road speed related electrical feed back signal used in vehicle control be reliable and steady, the above methods are not considered by the applicant to be satisfactory.
Finally it is obvious that vehicle engine speed related signals give difficulties in accurate translation to road speed where gearboxes are interposed between the engine and road wheels. Nevertheless engine speed can be usefully used in special applications and, in vehicles having no electrical ignition systems, the methods and means of this invention can conveniently be used. Also the method of this invention can be used where the rotating component is a toothed wheel in an existing vehicle gearbox or differential assembly.
All the above efforts to obtain something that will have wide general application for vehicle control have encountered difficulties through either unsatisfactory signal generation from existing magnetised components or through difficulties encountered in the closely adjacent location of the rotating vehicle component to the sensor which have heretofore been separated only by a very small air gap. This difficulty in location is accentuated by vibrations or relative movements between the sensor and rotating member where the latter is, for example, a drive shaft.